Project Summary/Abstract Cancer survivors often suffer from posttraumatic stress disorder (PTSD) symptoms as a result of their cancer diagnosis and treatment, which impair health outcomes such as quality of life (QOL). Although traditional office-based cognitive behavioral therapies (CBT) are effective, cancer survivors often lack access due to cost and distance barriers. At highest risk for persistent or worsening PTSD symptoms are low-income and/or nonwhite cancer survivors who received hematopoietic cell transplantation (HCT) as part of an aggressive cancer treatment. Mobile Health (mHealth) programs are increasingly used to facilitate access to CBT; some are self-guided and others require individualized, more intensive videoconferenced sessions with therapists. Hence, a continuum of mHealth CBT-based (mCBT) solutions with differing levels of intensity is available to support cancer survivors with PTSD symptoms. ?Right-sizing? treatment ensures optimal benefit without wasting resources such as patient time and healthcare costs. This grant application aims to answer the question: What is the right intervention solution for this cancer survivor at risk for, or suffering from, PTSD symptoms? We propose to construct and refine an adaptive (individually-tailored) mHealth approach for managing symptoms of PTSD in cancer survivors who recently completed autologous or allogeneic HCT therapy, including those who are most at risk for poor outcomes and have the greatest opportunity to benefit. Our research team is comprised of national leaders in the area, including the investigators who have defined the problem as well as devised potential mCBT solutions. One of these solutions is Cancer Distress Coach, a mobile application developed in partnership with the National Center for PTSD, as an effective self-management tool for addressing symptoms. It will be used with more intensive mCBT therapies that require individualized sessions with therapists to address these study aims: 1) Evaluate the effectiveness of Cancer Distress Coach relative to a control in reducing PTSD symptoms among HCT cancer survivors; 2) Assess treatment regimens embedded in the trial design for PTSD symptom reduction; and 3) Estimate tailored treatment regimens for PTSD and related outcomes that generate hypotheses about if, and how treatment should be tailored. These aims address symptom management - one of ten National Cancer Moonshort Initiative recommendations ? and the underserved have the greatest opportunity for benefit. Methods include using a Sequential Multiple Assignment Randomized Trial (SMART) to establish decision rules regarding when and in what way to intensify treatment for HCT cancer survivors (n=400) with Cancer Distress Coach and a more intensive mCBT. Electronic data collection surveys will be used and clickstream data captured to examine usage.